Voltarol gel

This is prob a really silly obscure question.Im trying this gel as latest attempt to relieve knee pain from moderate arthritis prescribed by doctor.Ive used it for 2 weeks and want to try another 2 to give it a fair trial.However i am not sure if it would be more effective applied to back or front if knee. Cant fi d anything online and I dont have an appointment for a month. . Any health experts able to advise? Also is it a cumulative drug?Thanks